The present invention concerns an electronic device for monitoring the temperature of a medium to be monitored and a method for implementing the same.
For numerous products, such as frozen food or certain pharmaceutical specialities, it is necessary to be able to check that a product, kept at a temperature lower than 0xc2x0 C., has not, at any time, been subjected to a rise in temperature above a predetermined threshold. Such products can, in fact, go bad and present a real danger to the consumer if they are not subject to a strict respect for the cold chain between the moments when they are frozen and when they are used.
There currently exist a multitude of warning devices, which indicate permanently and irreversibly whether a temperature has passed a fixed threshold.
Certain of these devices include, for example, a substrate made of paper, cardboard or other material, in the shape of a coloured tongue or disc covered with an opaque resin layer with a determined melting point. This resin is coloured in a different shade from that of the substrate as to cover the shade of the substrate.
If, following a rise in temperature, the resin melts, it flows away and allows the substrate to appear, the colour of the substrate being indicative and revealing that the resin melting temperature threshold has been reached or exceeded.
Other temperature monitoring devices include a material with calorimetric moisture detective agent qualities. This material, which may be a powder or crystals, has the property of changing colour on contact with water, passing for example from uncoloured to red. The calorimetric detective agent is placed in the presence of a liquid with antifreeze qualities such as a mixture of water and alcohol. It is the proportion of water and alcohol which will determine a precise solidifying and melting temperature for the mixture.
The device is placed as an indicator on the merchandise when it is cold stored (quick-frozen or deep-frozen). Provided the product and its indicator are kept at a temperature lower than the melting point of the antifreeze/water mixture, nothing happens since the ice has no effect on the calorimetric moisture detector. The indicator remains its initial colour.
However, if the merchandise and its indicator are brought to a temperature higher than the melting point of the antifreeze/water mixture, the ice begins to melt and the liquid comes into contact with the moisture detector. The indicator changes colour.
From then on, any new exposure to the cold, even higher than the solidifying point of the mixture, can in no way modify the colour of the indicator, which remains irreversibly changed.
Devices of the aforementioned type have to be applied to each item of merchandise and be accompanied, if required, by an explanatory note. They thus have the drawback of requiring an individual check of each device, either by the distributor for example, when the merchandise is received and at the moment that they are actually put on sale, or by the consumer himself, at the moment of purchase. Consequently, this check requires very particular care, whether by the distributor, by the person responsible for the counter where the merchandise is sold, or by the consumer. It also requires a relatively long checking time since each item of merchandise has to be individually checked.
Unfortunately, for economic reasons or simply by negligence, this check may appear too tiresome to certain distributors or wholesalers who do not take the time to check individually each of the articles which they sell. Thus, only certain articles will be checked, for example randomly, or, in the worst case, none of the articles will ever be checked. This results in a significant risk that the client will be deceived, and such deceit may even be carried out knowingly.
In practice, the aforecited indicator devices are only rarely used, because they only allow a check to be performed at the end of the chain, i.e. by the consumer, and because they are not sufficiently reliable.
Moreover, it should be noted that the known indicators are usually only intended for deep-frozen products, nothing having been provided for refrigerated produce such as dairy produce.
The object of the present invention is to overcome the aforementioned drawbacks in addition to others, by proposing an inexpensive electronic temperature monitoring device, which enables one to make sure, simply and efficiently, that the temperature has not, at any time, crossed a predetermined index value.
The present invention therefore concerns an electronic device for monitoring the temperature of a medium to be monitored enabling one to make sure that the temperature has not reached at least a pre-established index limit value, characterised in that it includes:
electrically conductive contact means able to close an electric charge flow circuit when said temperature reaches the or one of the index limit values;
electric charge storage means able to be connected to the charge flow circuit when the contact means close, the charges stored in these storage means being kept as long as the temperature does not reach its or one of its index limit values, and being able to flow through said charge flow circuit when the circuit is closed by said contact means, said storage means not returning to the charge state which they had before the charge circuit closed if the latter opens again, and
read means determining the charge state of said storage means.
As a result of these features, the present invention provides a totally passive electronic device for checking whether a temperature has experienced a rise beyond a fixed threshold. Indeed, during the entire temperature monitoring period, the electronic device according to the invention does not require any current or voltage supply to be able to operate, only the initial phase of injecting the electric charges into the storage means of said electronic device requiring the device to be powered.
After this first step of writing in the storage means, the electronic device thus operates in a totally autonomous manner. Affixed as an indicator to the product whose temperature has to be controlled, the electronic device keeps its initial state of electric charge provided that nothing happens, i.e. as long as the temperature does not reach its critical value. As soon as that value is reached, the contact means connect the storage means to the charge flow circuit, and the charges stored in said storage means instantly escape. Thus, the charge state of the storage means is indicative of temperature change during the monitoring period. If they are charged at their initial charge level, the storage means indicate, during the check, that the temperature has not undergone any variation capable of altering the qualities of the product to be monitored. Conversely, if a modification in the charge state of the storage means is observed during the check, this means that the temperature has reached its index value at least once during the monitoring period.
Advantageously, the modification in the charge state of the storage means is irreversible. If the temperature has momentarily reached, for example a maximum, and it returns to below this maximum before the check is carried out, the storage means will never return to their initial charge state, the charges being unable to flow back from the charge flow circuit to said storage means. The present invention thus provides an inviolable device in which the record of a temperature crossing an index value cannot be deleted or modified.
Finally, it is a variation in the electric charge and not, for example, a change of colour as is the case in the prior art, which indicates to the user that the temperature has reached its index value. This constitutes substantial progress insofar as appreciation of a colour is difficult and always subject to the observer""s subjectivity, such as the end consumer of the product, whereas an electric variable is an objective parameter which can be perfectly measured and quantified. Further, the values of an electric variable, current or voltage, can be stored in a computer and kept there indefinitely, for example for the purpose of statistical research.
According to another feature of the invention, the electronic temperature monitoring device can be associated with an electronic tag. Such electronic tags are well known to those skilled in the art. They are commonly used to distinguish and identify the objects to which they are affixed. Such tags are provided with a device for receiving and transmitting electromagnetic waves coupled to an electronic module for processing the received signals and retransmitting others able to include, for example, a message for identifying the tag, and thus the object to which it is affixed. Moreover, the system includes a reader including an electromagnetic wave transceiver device for transmitting data between a data terminal and said electronic tag.
The reader fulfils several functions, used in particular for:
transmitting to the tag the power necessary for it to function, the tag not having any specific autonomous power source;
transmitting to the tag data originating from the terminal, this data being able to be written in and out of a memory with which the tag is provided, and
receiving data originating from the tag and specific thereto, in particular for the purpose of identifying it.
In order to perform these various transmissions, the reader includes one or more antennae formed of coils, which are used for transmission and reception.
The tag also includes one or more antennae for receiving the electromagnetic waves transmitted by the reader, each of these antennae also being used for the transmission of data to the reader. In reception mode, the antenna or antennae form induction receiving means for energy originating from the reader, and means for receiving data transmitted therefrom. The antenna is connected to a processor including the means necessary for demodulating the signals received by the antenna, and for coding and modulating the signals to be retransmitted.
The tag provides, via its antenna, the energy necessary to power the read means of the electronic temperature monitoring device according to the invention. Moreover, as a result of the presence of these tags, the reader can simultaneously check a multiplicity of products to which the tags are affixed. It is thus no longer necessary to check the products one by one. Moreover, since the reader can read each tag""s identification message, it can very easily determine which articles have been exposed, even momentarily, to a temperature having reached the critical threshold. These products can then be rapidly withdrawn from the distribution chain.
Another advantage of the joint use of an electronic tag with the temperature monitoring device lies in the fact that, since the check of the storage means"" charge state is performed remotely, the monitoring device can be arranged inside the packaging containing the product to be preserved, rather than being simply added to the exterior of said packaging.
This constitutes another important advantage of the present invention. Indeed, the devices of the prior art which have to be visible in order to be able to be checked, and which are thus affixed to the outer packaging of the products, can indicate an entirely momentary heating which affects only the outer superficial part of the packaging and which is not damaging for the product to be preserved. Such a method is thus liable to cause significant quantities of products which have not been affected, to be rejected.
Other manufacturers have proposed placing an indicator in each deep-frozen packet and no longer on the outside thereof (on the packaging) as described hereinbefore. In this case, it is the consumer and only the consumer who, upon opening the deep-frozen article, can judge whether the indicator appears normal, the consumer being able to be guided by an explanatory note joined to the deep-frozen article.
In addition to the fact that observing the indicator cannot reveal with certainty whether or not the cold chain has been broken, the consumer may find himself in possession of food unfit for consumption which he will nonetheless have paid the seller for. In practice, this is unacceptable.
The present invention thus also concerns a method for implementing the electronic temperature monitoring device of the type described above, characterised in that it consists in:
writing data by injecting electric charges into the charge storage means;
placing the electronic device in the medium whose temperature evolution one wishes to monitor in order to ensure that this temperature has not reached at least one pre-established index limit value;
reading, in a non destructive manner, while the device is still in the medium to be monitored, the data written in the charge storage means, so as to determine whether or not the temperature of said medium to be monitored has, at a given moment, reached its or one of its pre-established index limit values, knowing that if the temperature has not reached its or one of its index limit values, the contact means have not closed and the charge state of the charge storage means has remained unchanged, whereas if the temperature has reached its or one of its index limit values, the contact means have closed and the charge state of the charge storage means has been modified, this modified charge state of the charge storage means being preserved even if the temperature of the medium being monitored again passes below or beyond the index value which it has reached and the contact means open again;
continuing or stopping temperature monitoring and, if necessary,
reprogramming the electronic temperature monitoring device in order to use it again.